Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $76.74   9.826%   $84.2805   $84.28   $84.30   $84.30  
  Purchase #2 $221.41   11.365%   $246.5732   $246.57   $246.55   $246.60  
  Purchase #3 $197.44   9.683%   $216.5581   $216.56   $216.55   $216.60  
  Purchase #4 $106.96   12.634%   $120.4733   $120.47   $120.45   $120.50  
  Purchase #5 $19.57   3.723%   $20.2986   $20.30   $20.30   $20.30  
  Purchase #6 $22.81   9.482%   $24.9728   $24.97   $24.95   $25.00  
  Purchase #7 $240.56   11.721%   $268.756   $268.76   $268.75   $268.80  
  7 purchase totals = $885.49       $981.9125   $981.91   $981.85   $982.10